An example of a part included in an internal combustion engine such as a gasoline engine of an automobile is a spark plug. Such a spark plug typically includes a cylindrical insulator, a main body metal fitting which holds the insulator, a rod-shaped center electrode which is held in the insulator and a leading end of which is exposed from an end of the insulator, a ground electrode that is welded to the main body metal fitting, and a terminal metal fitting disposed on another end of the insulator. The ground electrode is formed so as to have an L-shape and is attached to the main body metal fitting such that a short strip thereof faces an exposed end face of the center electrode. Nickel-based metals such as pure nickel and nickel alloys are used as the materials constituting the center electrode and the ground electrode.
One characteristic desired for a constituent member of an internal combustion engine, such as an electrode of the spark plug, and a raw material thereof is that particles are not easily generated on the surface of the constituent member or the raw material as a result of use over time (paragraphs [0010], [0011], etc. of the specification of PTL 1). These particles are formed as a result of a phenomenon in which the material constituting an electrode or the like is melted and then solidified in the form of spherical projections. The particles are composed of a mixture containing elements in an atmosphere, the elements being derived from engine oil or the like, and Ni (nickel), which forms a matrix of the electrode (paragraph [0010] of the specification of PTL 1). When a large number of such particles are generated on a surface of an electrode, in particular, when a large number of such particles are generated, and furthermore, grown to become coarse particles in a portion where spark discharge is performed (mainly on surfaces of the center electrode and the ground electrode that face each other), the ignition state of an engine may become unstable or, in the worst case, the particles may be detached and may damage the engine.
Accordingly, it is desirable to examine the ease of the generation of particles or the difficulty of the generation of particles. PTL 1 discloses equipment including a gasoline engine for testing, the equipment being used for examining the degree of the generation of particles (paragraph [0055] of the specification).
With regard to constituent members of an internal combustion engine and raw materials thereof, an engine for testing is usually used also in the case where characteristics other than the ease of the generation of particles are examined (for example, paragraph [0055] etc. of the specification of PTL 2).